Webs in the form of magnetically-coated tapes have been used for several years for recording digital data received from data processing equipments of all types. Additionally, such webs have been used for audio and video applications as well. For data processing applications, it is desired that access to data recording areas on the web occur rapidly. To this end, so-called vacuum columns, such as shown in Weidenhammer, et al, U.S. Pat. Nos. 3,057,568 and 3,057,569, are employed to provide a buffer between web or tape containing reels and a transducing or work station. The arrangement is such that a capstan rapidly accelerates the web to provide the rapid access with the vacuum columns providing a low inertial length of web for permitting rapid acceleration and the resulting rapid access. The vacuum columns decouple the work station from the reel of tape such that a relatively short length of the web could be accelerated while the reel was being rotationally accelerated. In this arrangement, the bight of the web formed in the vacuum column varied in length as the reel inertia was compensated for. Typically, during stop-start motions of such a web handler, the length of the bight in the vacuum column varies dramatically. An improvement over the Weidenhammer, et al, vacuum column is shown by Wicklund, et al., U.S. Pat. No. 3,112,473 wherein the walls of the vacuum columns are tapered such that as the bight became longer it also became narrower, which decreased the pull on the web. A later tapered column is shown in Epina, et al, U.S. Pat. No. 4,189,113. Wicklund, et al, also teach that a plurality of vacuum columns interposed between a work station and a web containing reel provide certain advantages in mechanically buffering the reel from the work station. Other forms of secondary buffers are shown by Reader, U.S. Pat. No. 3,202,373 and Schoeneman, U.S. Pat. No. 3,176,894. All of these improvements over Weidenhammer, et al, were directed toward improving the access to data areas on the web by using a vacuum column as a web buffer storage.
Various designs of web vacuum buffer storage apparatus have been employed for not only providing the buffer storage, but also for controlling the bight in the buffer storage and performing auxiliary web-controlling functions. Dickinson, et al in U.S. Pat. No. 3,645,470, show an air passageway extending between two side-by-side vacuum columns to serve as a clamp, such that when a web is loaded into the vacuum columns it will load into both columns. The clamp limits the slip of the web over a capstan such that the web enters both vacuum columns. This control limits the transport of the web between adjacent vacuum columns during the loading process. In this arrangement, a work station or transducer station was integral to one of the vacuum columns. Grant, in U.S. Pat. No. 3,986,651, shows a symmetrical web transport arrangement wherein concave vacuum assisted guides are used for guiding the web past a work or transducer station with vacuum columns stabilizing the flow of tape, i.e. decoupling the capstan from the web containing reels. Grant, in U.S. Pat. No. 3,281,040, also shows a vacuum assisted guide wherein slots along the guides permit air flow for controlling the web within the vacuum chamber guide. Stange, in U.S. Pat. No. 4,218,026, shows a vacuum arrangement with an adjustable side, ostensibly for taking various widths of webs. Welch, in U.S. Pat. No. 3,266,691, shows a series of tapered vacuum loop boxes such as originally taught by Wicklund, et al, supra, for preventing breakage of the web during rapid acceleration-deceleration. Hawley, in the IBM Technical Disclosure Bulletin, Feb. 9, 1975, on page 2567 in an article entitled "Contour Vacuum Column," shows a flexible shim and a shaped side wall in a vacuum column for accommodating slewing of the web during transport for providing guiding of the web toward a work station. Tape tension control also has received attention by Janssen, et al in the IBM Technical Disclosure Bulletin, February, 1975, page 2564 wherein a so-called soft vacuum pocket redistributes tension uniformly across the tape. The soft vacuum pocket is bracketed in the tape path by a pair of air bearings. The tape tension redistribution device eliminates non-uniform stresses or tensions in the tape, which, among other things, accommodates skewing caused by misaligned reels. Such skewing appears in the tape as a curvature between the two misaligned reels.
In a high performance reel-to-reel web transport, such as used in a reel-to-reel magnetic tape recorder, uniform tension is applied to the web during rapid acceleration-deceleration. Standing waves can be induced into the web such that there are differing tape tensions along the tape path between the reels. Further, as the wrap of the web on either of the reels varies, the angle of approach from the reel to the web transport path changes. This change in angulation can affect the length of web disposed between the reel and a work station and disposed between the two reels in the reel-to-reel transport. Further, the web may have a lateral curvature induced from being stored on a reel. All of these factors could be accommodated before the web is transported past the work station while maintaining the length of the web between a reel and a work station to be substantially constant. While the vacuum column buffers of the prior art provide for good mechanical buffering, such buffers require substantial space and are costly. Therefore, it is desired to eliminate the vacuum buffers while still maintaining good control over the web during acceleration and deceleration. When a web 15, such as a magnetically coated plastic substrate recording tape, is stored on a reel, such storage may result in certain undesirable shape changes (tape may curl laterally); for reliable magnetic recording operations, such changes should be accommodated within a short distance of the supply reel. Such accommodation could minimize tape transport length for a reduced cost recorder.